1. Field of the Invention
The present invention relates to a vehicle power steering control apparatus for assisting a steering torque, which is generated by a steering operation of a driver, by an electric motor and a control method of the same.
2. Description of the Related Art
This kind of conventional power steering control apparatus includes, for example, as disclosed in JP-B-6-59834 (page 6, FIG. 5), a torque sensor for detecting a rotation force of a steering wheel of a vehicle, a vehicle speed sensor for detecting a vehicle speed, a motor supplied with electric power from an in-vehicle battery and for transmitting an auxiliary torque to a steering system, and a power element part for controlling the flowing current and flowing direction of the motor. The power element part is controlled in accordance with signals of the torque sensor and the vehicle speed sensor, and when the motor current is zero at the time of energizing instructions of the motor current, a power element is judged to be opened, and the power element part is interrupted to prevent a defective steering from being generated when the power element is damaged.
However, the failure judgment condition as stated above is established also in a case where for example, a driver abruptly steers the steering wheel, a counter electromotive force is generated since the motor is rotated, and the motor current becomes excessively small by the counter electromotive force. Thus, there has been a problem that in order not to erroneously detect a failure, a failure judgment time must be set to be sufficiently long (for example, 5 sec).
Besides, when a motor current detection circuit goes wrong, not only the controllability of a motor current control part is deteriorated, but also a motor target current itself determined using a current detection value as one of inputs becomes an abnormal value. Thus, there has been a problem that the steering assist characteristic to the steering of the driver is further deteriorated.